Overall, preterm birth occurs in 1 of every 8 births in the US (March of Dimes; PeriStats), and preterm labor accounts for almost half of those delivered preterm. Prematurity is responsible for $25 billion per year of health expenditures in the US. Health care providers currently must decide whether to transport patients or treat preterm contractions based primarily on the strength and frequency of contractions and the cervical exam. Frequency can be precisely measured using the tocodynamometer (toco), which measures the shape change of the uterus. Studies have assessed uterine contractions and their relationship to labor; see for example Csapo A., Obstet Gynecol. Surv. 1970; 25:515-43, and Ramon C., et al. Biomed Eng Online 2005; 4:55. Other investigators have looked at propagation of contractions across the uterus in efforts to identify labor stages; see for example Lucovnik, M., et al. Acta Obstet Gynecol. Scand. 2001 February; 90(2):150-157; Lucovnik, M., et al., Am J Obstet Gynecol. 2011 March; 204(3):228e1-228.10; and Schlembach, D. et al., Eur J Obstet Gynecol. Reprod Biol. 2009 May; 144 Suppl 1:S33-9. Epub 2009 Mar. 17. But non-invasive, accessible, accurate, and inexpensive methods to determine labor status remain elusive.
Clinically, a diagnosis of preterm labor is currently made by considering only the frequency and strength of contractions and the cervical exam, which does not permit an accurate assessment of whether or not a subject is in true labor. Some women seem to experience strong, relatively frequent contractions but the contractions do not change their cervix. Others experience cervical change with only infrequent, moderate contractions. Thus, measuring frequency and strength of contractions does not permit accurate assessment of labor status.